delta=0.1;
side=10+2*delta;
height=3*side;
width=5*side;
plate_height=2;

chamfer=2.5;
linear_extrude(height = plate_height)
    difference(){
        union(){
            square([width-2*chamfer,height],center=true);
            square([width,height-2*chamfer],center=true);
            for(a=[-1,1])
                translate([(width/2-chamfer)*a,(height/2-chamfer)*a,0])
                    circle(chamfer,$fn=100);
            for(a=[-1,1])
                translate([-(width/2-chamfer)*a,(height/2-chamfer)*a,0])
                    circle(chamfer,$fn=100);
        };
        
        translate([0,-side/2,0])
            polygon([[0,side],[side/2,0],[-side/2,0]]);
        
        translate([-side*1.3,0,0])
            circle(side/2,$fn=250);
        
        translate([side*1.3,0,0])
            square(side,center=true);
    }